1. Field of the Invention
The present invention generally relates to optical systems, and more particularly to an improved optical system for use with traffic signal devices.
2. Description of the Prior Art
Typically a traffic signal optical system includes a lamp, a lens and a reflector contained within a traffic signal housing. A conventional power specification or power rating for the lamp is directly related to the diameter of the lens. For example, a nominal power rating of 150 Watts is used for a 12 inch (300 mm) diameter lens and a nominal power rating of 60 Watts is used for a 8 inch (200 mm) diameter lens. The lamps most commonly used are 165 Watt and 67 Watt, incandescent standard 8,000 hour, providing 1950 and 625 initial lumens, respectively.
Conventional lenses are convex with smooth exterior and prismatic interior surfaces, pressed or molded of an appropriate color transmitting glass or plastic material. Due to the temperatures resulting from the required high power lamps, plastic lenses are formed of a high temperature resistant material, usually polycarbonate, rather than a more optically efficient acrylic.
Known reflectors typically are shallow parabolas, limited in depth by the relatively short available space behind a lens gasket on a signal door of the traffic signal housing. Conventional reflectors generally are formed of bright anodized aluminum and metalized polycarbonate, while some earlier reflectors were formed of silvered glass. A required controlled light output of approximately 600 lumens is provided by various known signal systems utilizing a 1950 lumens, 165 Watt incandescent lamp.
While known traffic signal devices provide generally satisfactory operations, it is desirable to provide an optical system for traffic signal devices having improved control of the emitted light for increasing the efficiency to achieve the required lumen output with significantly reduced power requirements. It is further desirable to provide such an optical system that reduces the sun phantom effect of known traffic signal devices. The sun phantom effect is the illusion that a signal face is illuminated when the sun's rays are nearly perpendicular to the face of the lens.